Triode sputtering apparatus

ABSTRACT

A triode sputtering apparatus to deposit material on the surface of an article. The apparatus comprises an enclosure means for evacuating the enclosure, a means for establishing an ion plasma in the enclosure. An ion target, including two members with surfaces of the material to be sputtered, is located in the enclosure with the surfaces facing the ion plasma. The target members are electrically biased so that ions from the plasma will impinge on their surfaces and sputter material therefrom. An article having a surface to be coated is mounted in the enclosure so that the surface faces the ion plasma and the sputtering surfaces of the target which are at an acute angle to the surface of the article. An electron funnel is used to funnel electrons being supplied to the plasma between the article and the target and an elongated anode is used to attract electrons from the plasma. The apparatus may be used to coat 11 by 11 inch glass plates with a metallic layer having substantially uniform optical density.

nited States Patent [1 1 Vegh et a1,

[ Dec. 18, 1973 [73] Assignee: Eastman Kodak Company,

Rochester, NY.

22 Filed: Oct. 26, 1971 21 Appl.No.: 192,585

Related US. Application Data [63] Continuation of Ser. No. 817,635, April 21, 1969,

abandoned.

[52] US. Cl. 204/298, 204/192 [51] Int. Cl. C23c 15/00 [58] Field of Search 204/298, 192

[56] References Cited UNITED STATES PATENTS 3,325,393 6/1967 Darrow et al 204/298 3,393,142 7/1968 vMoseson 204/298 FOREIGN PATENTS OR APPLICATIONS l,428,243 l/1966 France 204/298 OTHER PUBLICATIONS Michalak, Low Energy Sputtering of Resistive Films," Vacuum, Vol. 17, No. 6.

Primary Examiner-Howard S. Williams Assistant Examiner-Sidney S. Kanter Attorney-William T. French et a1.

[5 7] ABSTRACT A triode sputtering apparatus to deposit material on the surface of an article. The apparatus comprises an enclosure means for evacuating the enclosure, a means for establishing an ion plasma in the enclosure. An ion target, including two members with surfaces of the material to be sputtered, is located in the enclosure with the surfaces facing the ion plasma. The target members are electrically biased so that ions from the plasma will impinge on their surfaces and sputter material therefrom. An article having a surface to be coated is mounted in the enclosure so that the surface faces the ion plasma and the sputtering surfaces of the target which are at an acute angle to the surface of the article. An electron funnel is used to funnel electrons being supplied to the plasma between the article and the target and an elongated anode is used to attract electrons from the plasma. The apparatus may be used F to coat 1 1 by 1 1 inch glass plates with a metallic layer having substantially uniform optical density.

2 Claims, 4 Drawing Figures PMENTEBBEC18 m5 v 3.779.891

lsnht l 1 BF 2 ALFRED E. COATES BERTALAN J. VEGH INVENTORS WWW A T'TORNEYS PAIENTEDUEB 18 I915 3.779.891

ALFRED E. COATES BERTALA/V J VEGH INVENTORS A TTORNEYS TRIODE SPUTTERING APPARATUS This is "a 'continuation, of application Ser. No. 817,635, filed Apr. 21, 1969. Y

The present invention relates to sputtering, and, particularly, to an improved apparatus for depositing thin films of material on'the surface of an article by sputtermg.

Various forms of the sputtering apparatus have been used to deposit thin films of material on the surface of articles or substrates. Such an apparatus is disclosed in US. Pat. No. 3,305,473. This apparatus comprises an enclosure, means for evacuating the enclosure, and means for establishing in the enclosure an ion plasma extending substantially along a predetermined axis. An ion target having a surface of the material to be sputtered is located in the enclosure with the surface spaced from and extending substantially parallel to the ion plasma axis. The ion target is electrically biased so that ions from the plasma will impinge in the ion targets surface and sputter material therefrom. A substrate is mounted in the enclosure so that the surface of the substrate on which sputtered material is to be deposited faces the ion plasma axis and the abovementioned surface of the ion target. The apparatus may include means for establishing in the enclosure a magnetic field for controlling the density of ions at the target so as to achieve a uniform deposition of sputtered material on the substrate or a sputtered film having a desired gradient or gradients of thickness which respect to a plain through one surface of the film. While the above apparatus is suitably adapted for the uniform deposition of sputtered material on relatively small, e.g., 4 inches by 4 inches planar surfaces, it has been found that the apparatus does not provide sufficient control to achieve a uniform deposition of sputtered material on substantially larger surfaces, e.g., 8% by 8% inch plates. We have discovered ways and means of obtaining a more uniform deposition on such larger substrates.

Accordingly, an object of the present invention is to provide improvements in the above-mentioned triode sputtering apparatus whereby more uniform deposition of sputtered material can be accomplished.

Another object is to provide an improved apparatus of the above-described type wherein an anode and cathode for the ion plasma are modified for controlling the uniformity of deposition of sputtered material on the substrate.

Still another object of the present invention is to provide an improved apparatus of the above-described type wherein a sputtering surface of the ion target is disposed in an angular relationship with the surface of the article or substrate to control the uniformity in the depositionof sputtered material on the surface.

Another object of the present invention is to increase the effectiveness of existing sputtering apparatus to coat larger surfaces. I

A further object of the present invention is to provide an apparatus of the above-described type wherein substrates as large as 8% inch and ll inch square can be provided with chromium coatings having substantially uniform optical density.

Other objects and'advantages of the present invention will be apparent to those skilled in the art by the description of preferred embodiments of the invention which follows.

The objects of the present invention are accomplished by providing a triode sputtering apparatus wherein the target includes two members each having at least one substantially planar surface disposed at an acute angle to the planar surface of the substrate. Also provided are means to form the ion plasma of a triode sputtering device in such a manner that depositions of sputtered material on the substrate will be controlled.

Reference is now made to the accompanying drawings wherein like reference numerals and characters designate like parts and wherein:

FIG. 1 is a diagrammatic sectional elevation view showing one embodiment of the improved triode sputtering apparatus according to the present invention.

FIG. 2 is an enlarged side view of a V-shaped, Z-piece target and the geometric relationship of the target's surfaces to an 1 l X 11 inch substrate to be coated, the anode and the electron funnel according to one embodiment of the present invention.

FIG. 3 is an enlarged side view of a modified V- shaped, two piece target and the geometric relationship of the targets surface to an I l X l 1 inch substrate, the anode, and the electron funnel according to another embodiment of the present invention.

FIG. 4 shows top, elevation, and side views of the electron funnel shown in section in FIG. l.

The present invention involves improvements of various elements of an apparatus disclosed in the aforementioned U.S. Pat. FIG. 1, which shows portions of this known apparatus, discloses the relation of the present invention therewith. It is intended that the disclosure of US. Pat. No. 3,305,473 to Moseson be incorporated in the present application.

The sputtering and film-depositing apparatus 10 shown in FIG. 1 comprises a base 111 and a removable bell jar 14 located on base 11 and sealed thereto at an annular structure 15. Acathode filament 14 is disposed beneath the base 111. A tubular filament shield 32 sur rounds the filament and communicates with the interior of bell jar 14. A baffle plate 50 encompasses the upper end of filament switch 32. Mounted (means not shown) within the bell jar is an anode 68, an ion target 94, a substrate 93 and an electron funnel 33. During operation of apparatus), filament 41 releaseselectrons to the anode surface 70. These electrons collide with gas molecules present in the bell jar 14. The gas molecules are thus ionized and an ion plasma forms in the space between the anode 68 and the electron funnel 33. The ion target 94 is electrically biased (means not shown) so that ions from the plasma are attracted to the targets surface 95'and sputter material therefrom to surface 190 of substrate 99.

FIG. 2 depicts one embodiment of the inventive improvements for the type of apparatus disclosed by Moseson. FIG. 2 shows a target 94 consisting of two flat pieces each 12 inches long by 6% inches wide, placed, as shown, at a interior angle to each other. The electron funnel 33 converts the flow of electrons radiating from the cathode filament 41 and forces them to rent electric power supply in a manner and by means similar to those described by Moseson. A A; inch insulating space between the two pieces of target 94 prevents arcing. The geometric relationship of the substrate surface 100 to be coated to the other components are shown in FIG. 2.

FIG. 3 depicts another embodiment of the novel improvements for the type of apparatus disclosed by Moseson. FIG. 3 shows a modified V-shaped target 94 consisting of two pieces, each 12 inches long. Each piece consists of a 4% inch wide flat section attached to a 2% inch wide flat section at an interior angle of 160. The two pieces are placed, as shown, at a 135 interior angle to each other with a A; inch space between the pieces to prevent arcing. The electron funnel 33 and anode 68, as described in connection with FIG. 2, are used with the modified V-shaped target. The geometric relationship of the substrate surface 100 to the other components are shown in FIG. 3.

FIG. 4 shows the preferred configuration of the electron funnel 33 according to the present invention. Such a funnel can be fabricated from heat resistant materials such as stainless steel or glass according to known methods. As shown in FIG. 4, electron funnel 33 has an elongated outlet 34 and a circular inlet 35. The outlet 34 is about ll inches long and k inch wide and the inlet 35 is dimensioned so that it can be received within the upper end of tubular filament shield 32 which in the present disclosure is about 2 inches in diameter.

The target, substrate, etc., configuration of FIG. 2 has been used to deposit chromium in a triode sputtering apparatus. Using the geometry of FIG. 2, the chromium coating of the substrate was accomplished at an absolute argon gas pressure of 0.75 microns; a positive D.C. potential of 80 volts (4.5 4.9 amperes) on the anode; a negative D.C. potential of 900 volts (230 milliamperes) on the top piece of the target; a negative D.C. potential of 500 volts (220 milliamperes) on the bottom target piece. The optical density nonuniformity of the chromium coatings on I] by l 1 inch glass substrate, deposited under the conditions described, did not exceed percent. This percentage was determined by measuring the optical density over the area of the coated substrate, subtracting the minimum optical density reading from the maximum reading, dividing this difference by the minimum optical density reading, and multiplying that result by 100. With reference to FIG. 2, an 8% by 8% inch glass substrate was centered in the position previously occupied by the l l X ll inch glass plate and coated under the conditions described above-The optical density nonuniformity of the chromium coating on the 8% by 8% inch plate did not exceed 13 percent.

The geometrical configuration of FIG. 3 has been similarly used to coat chromium on the surface of glass substrates. The chromium coating was accomplished at an absolute argon pressure of 0.75 microns; a positive D.C. potential of 80 volts (4.8 amperes) on the anode; a negative D.C. potential of 800 volts (310 milliamperes) on the top target piece; a negative D.C. potential of 700 volts (200 milliamperes) on the bottom target piece. The optical density non-uniformity of the chrome coatings on the II by ll inch glass substrate deposited under these conditions did not exceed 12 percent. With reference to FIG. 3 an 8% by 8% inch glass substrate was centered in the position previously occupied by the l l by I 1 inch plate and coated at same conditions. The optical density non-uniformity of the chrome coating on the 8% by 8% inch plate did not exceed 9 percent.

The results for optical density when using the geometric configurations of FIG. 2 and FIG. 3 were evaluated over a range of absolute optical densities from 1.5 to 3.5. Thus, for example, in the last stated example, the non-uniformity of the coating on the 8% by 8% inch substrate was found to be in a range from 1.5 plus or minus 9 percent to 3.5 plus or minus 9 percent.

It has been found that the optical density uniformity of metallic coatings on large glass substrates is dependent upon several factors, which are: (1) the shape of the metallic target; (2) the shape of the electron funnel which controls the flow of electrons into the sputtering region; (3) the shape of the anode which attracts and accelerates the electrons thereby causing ionization of the inert gas, argon, which is the sputtering agent; (4) the geometric relationship and placement of the target, substrate,'anode and electron funnel each with respect to the other; (5) the absolute pressure within the sputtering chamber; and (6) the magnitude of the positive and negative voltages, respectively, placed on the anode and the two pieces of the ion target. The conditions described above in regard to the examples, are those which resulted in the optimum optical density uniformity of chromium deposited on the various substrates. However, it has been found that slight modifications of the shape of the anode and electron funnel do not result in significant changes to the optical density uniformity of chromium coatings. Specifically, with reference to FIG. 3, l l by l 1 inch glass substrates were coated as depicted and described previously but with the anode length reduced from 13 to l 1 inches and the electron funnel length rendered from 11 to 10 inches. The optical density uniformity was not appreciably affected. Thus, it has been found that of the six parameters noted above as affecting optical density uniformity, four have been found to be more significant than the others. These four are the shape of the ion target, the absolute pressure, the magnitude of the applied voltages, and the geometric relationship of the substrate with respect to the ion target. The other parameters, namely anode shape, electron funnel shape, and the exact location of these components with respect to the substrate and target, can be varied to a limited extent without affecting the optical density uniformity of resulting coatings.

The targets described above consisted of a stainless steel support with a high purity chromium deposit on the sputtering surface 95. It should be understood that other constructions could be used without departing from the scope of the present invention. For example, it has been found that a A inch sheet of high purity chromium bonded to an aluminum backing with epoxy adhesive is also suitable for the present invention. It should also be apparent that the geometric shapes described in regard to the coating of chromium on substrates, could be utilized to apply other coatings such as gold, aluminum, tantalum, tungstun, silicon, germanium to surfaces of various articles.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

We claim:

1. In a triode sputtering coating apparatus for coating a. a container;

a surface of a substrate, said apparatus including: b. means for establishing an electron discharge to aa Container; provide an ion plasma in said container, said means means for establishing an electron discharge to including cathode means in spaced relation with an provide an ion plasma in said container, said means 5 anode; the improvement which comprises; including cathode means in sPaced relation with c. first and second target electrodes, said target elecanode; the mprovement whch compnses: trodes being spaced from each other and inclined c. first and second target electrodes, said target electrodes being spaced from each other and inclined relative to each other at an obtuse angle; 10

(1. means for supporting a substrate opposite said target electrodes and subtending said obtuse angle whereby material can be sputtered from the targets onto a substrate mounted on said support means;

relative to each other at an obtuse angle, said second target electrode being positioned closer to said anode than saidfirst target electrode;

d. means for supporting a substrate opposite said target electrodes and subtending said obtuse angle whereby material can be sputtered from the targets and e. electric bias means for establishing a first predeterand mined negative potential on said first target Surface e. electric bias means for establishing a first predeterand a second predetermined negative potential on mmed negatwe potentlalon Sald target Su 1'faCe said second target surface, one of said negative poand a Second predetermmednegauve potenilal tentials being greater than the other said negative Sald Second target Surface, aid Second negative popotential. tential being greater than said first negative poten- 2. In a triode sputtering coating apparatus for coating tial. a surface of a substrate, said apparatus including:

onto a substrate mounted on said support means; 

2. In a triode sputtering coating apparatus for coating a surface of a substrate, said apparatus including: a. a container; b. means for establishing an electron discharge to provide an ion plasma in said container, said means including cathode means in spaced relation with an anode; the improvement which comprises: c. first and second target electrodes, said target electrodes being spaced from each other and inclined relative to each other at an obtuse angle, said second target electrode being positioned closer to said anode than said first target electrode; d. means for supporting a substrate opposite said target electrodes and subtending said obtuse angle whereby material can be sputtered from the targets onto a substrate mounted on said support means; and e. electric bias means for establishing a first predetermined negative potential on said first target surface and a second predetermined negative potential on said second target surface, said second negative potential being greater than said first negative potential. 